The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This invention relates to oil and gas industry, particularly, to methods of reservoir stimulation during production and to methods of proppant flowback control.
A serious problem in oil production is flowback of proppant from the fracture back to the well: this happens after hydraulic fracturing of formation, during the first cleanup, and sometimes after well completion. The literature data show that up to 20% of the pumped proppant is usually removed from a fracture during fracture cleanup and production, and this causes several adverse consequences. In wells with a low production rate, the removed proppant may deposit on the casing; this situation requires regular cleanup and makes costly the repair operations. Another problem that can be caused by high proppant flowback rate is a failure or fast depreciation of electrical submersible pumps (ESP). Proppant flowback reduces the fracture conductivity due to fracture thickness loss; this reduces the well production rate.
There exist several known methods for proppant flowback control.
A widespread method is based on using a proppant with curable resin coating which is pumped to the fracture at the final stage of fracturing treatment. But the application of this proppant is restricted by secondary reaction of the resin coating with the fracturing fluid. These reactions cause partial degradation of resin coating and reduce the strength of bonding between RCP particles and the strength of the proppant packing. Besides, chemical reaction between the resin coating and fracturing fluid results in uncontrollable changes in the fluid rheology; this also affects the hydrofracturing efficiency. All the listed factors and cyclic loading caused by well opening/closure may be detrimental for the proppant packing strength.
A mixture of proppant with adhesive polymer materials can be used for proppant flowback control. Adhesive material comes in contact with proppant and makes a thin and tacking coating. This material facilitates adhesion between particulate and sand or/and crashed fines; this stops completely or partially the proppant flowback from the fracture. The typical feature of adhesive coating is that particles remain tacky for a long time even at elevated downhole temperatures without cross-linking or solidifying.
Adhesive materials can be matched with other reactants used in the hydrofracturing treatment, e.g., with inhibitors, bactericide agents, gel breaker, paraffin and corrosion inhibitors.
The U.S. Pat. No. 7,032,667 teaches about fracture propping with use of tacky agents and resin-coated proppant.
The U.S. Pat. No. 6,742,590 discloses the method of proppant flowback control by mixing of tacky materials with deformable particles (every component is already effective tool for flowback control).
Another kind of material suitable for proppant flowback control is thermoplastic materials. Thermoplastic compound is mixed with proppant, then it melts at a higher subterranean temperature and sticks to proppant; this creates aggregates of adhered proppant.
The U.S. Pat. No. 5,697,440 describes the method of application of thermoplastic material with resin-coated proppant.
The U.S. Pat. No. 6,830,105 teaches about the method for proppant flowback control, wherein the thermoplastic elastomer is mixed with proppant as a liquid (or a solution with appropriate solvent). Then the dissolved elastomer is cured independently or with curing agent producing a thermoplastic coating.
The U.S. Pat. No. 5,330,005 describes the method for proppant flowback control through mixing of a regular proppant with fiber material. Fibers intermingle with proppant pack and reduce flowback. Besides the strengthening of the proppant pack, added fibers redistribute the loads, making bridges on the most part of proppant pack area. A fiber-hold structure is more flexible than that composed of resin coated proppant: it allows small shifts in the proppant-fiber packing without loss in strength.
One approach is a fiber bundle of 5 to 200 separate fibers collected with the length from 0.8 to 2.5 mm and the diameter ranging from 10 to 1000 microns. These bundles are usually fixed at one end.
Mechanisms of using deformable, thermoplastic, and elastomeric materials for proppant flowback control is based on indenting of proppant particulate into deformable material. U.S. Pat. No. 6,059,034 describes deformable beaded particulate. Deformable particulate facilitates effective redistribution of stresses inside the packing, and improves the packing strength due to a higher contact area between the particles. A serious drawback of this soft material in a significant reduction in the free pore space in particulate packing because particles penetrate the pores and reduce the fracture permeability and, ultimately, the well production.
On another side, if we take a hard material, this is better for packing permeability, but also reduces the solid proppant penetration into the deformable material. The result is a lower strength of packing and danger of proppant flowback.